MATERIALS AND METHODS

Transcription

1 CHAPTER 3 MATERIALS AND METHODS 3.1 Materials Nitrile rubber (NBR) The material used as matrix in this study is nitrile rubber (NBR). Two grades of NBR were used and their properties are given in Table 3.1. Nitrile rubber used in the study of properties of various nanocomposites was APARENE N-0685B, a medium acrylonitrile (ACN) content NBR supplied by Apar Industries Ltd., Mumbai, India. In the product development studies, the nitrile rubber used was JSR 230SL, manufactured by JSR Corporation, Japan. Table 3.1 Properties of NBR Property APARENE N-0685B JSR 230SL Colour Light tan Light tan Volatile matter, % 0.70 max 0.70 max Ash, % 0.50 max 0.50 max Bound ACN, % Specific gravity Mooney viscosity of ML 1+4 at 100 C Nanoclay In the preliminary studies, four different grades of nanoclay, procured from Southern Clay Products, USA, were used. Their properties are given in Table 3.2. For detailed study, the nanoclay used was Cloisite 20A, a natural montmorillonite modified with quaternary ammonium salt (organic modifier - dimethyl dehydrogenated tallow, quaternary ammonium). The chemical formula for montmorillonite is 60

2 (Na,Ca) 0.33 (Al,Mg) 2 Si 4 O 10 (OH) 2.nH 2 O having molecular weight of The chemical structure of the organic modifier is Table 3.2 Properties of nanoclay [273] Nanoclay Cloisite Na + Cloisite 10A Cloisite 20A Cloisite 30 B Organic modifier None 2MBHT (dimethyl, benzyl, hydrogenated tallow, quaternary) 2M2HT dimethyl, dehydrogenated tallow, quaternary ammonium MT2EtOT (methyl, tallow, bis-2- hydroxyethyl, quaternary ammonium) Modifier concentration (cation exchange capacity) 92.6meq/100g clay 125 meq/100g clay 95 meq/100g clay 90 meq/100g clay % Moisture < 2% < 2% < 2% < 2% % Weight loss on ignition 7% 39% 38% 30% Typical dry particle sizes 10% less than: 2µ 2µ 2µ 2µ 50% less than: 6µ 6µ 6µ 6µ 90% less than: 13µ 13µ 13µ 13µ Density Loose bulk, lbs/ft Packed bulk, lbs/ft Specific gravity, g/cc XRD d 001 =11.7Å d 001 = 19.2Å d 001 =24.2Å d 001 =18.5Å 61

3 3.1.3 Nanocalcium carbonate Nanocalcium carbonate (NCC) is isodimensional nanofiller with all the three dimensions in the nanometre regime. Nanocalcium carbonate of average particle size 40 nm was provided by KPS Consultants, New Delhi, India. Other properties of nanosize calcium carbonate are given in Table 3.3. Table 3.3 Properties of nanocalcium carbonate Property Value Moisture, % <0.6 Bulk density, gm/ cc Whiteness, KETT C ph Average particle diameter, nm 40 Specific gravity 2.52 Oil absorption, ml/100g CaO, % 54 MgO, % 0.2 SiO 2, % 0.1 Iron and aluminium Oxide, % 0.2 Ignition loss, % Carbon nanotube Bundled multiwall carbon nanotubes (CNT) containing % single-wall CNT and double-wall CNT were used in this study. CNT of grade LB-MWT-10 was sourced from Shenzhen Nanotech Port Co. Ltd., China. The properties of CNT are given in Table

4 Table 3.4 Properties of bundled - multiwall carbon nanotube Property Purity, % Value > 90 (mainly 3~5 walls) Diameter, nm < 10 Length, μm 5-15 Amorphous < 5% Ash, % 2 Specific surface area, m 2 /g Compounding ingredients Vulcanising agents The vulcanising agent used in the investigation of properties of NBR nanocomposites was sulphur. Chemically pure grade of elemental sulphur (purity 99.6 % min) was obtained from Samira Chemicals, Coimbatore, India. For product development studies, in addition to sulphur, two grades of dicumyl peroxide (DCP -[C 6 H 5 C(CH 3 ) 2 O] 2 ) was used. In the first phase of study, UC-40 grade of DCP having 40±1 % purity supplied by Usha Chemicals, Pune, India was used. In the second phase, DCP of 99 % purity was used as vulcanizing agent. It was supplied by Anand Chemical Corporation, Chennai, India Accelerators (a) Dibenzothiazole disulphide (MBTS) Dibenzothiazole disulphide (MBTS) is a primary accelerator having the structure 63

5 MBTS [melting point C, loss on drying 0.39%, ash content 0.18%, fineness (100 mesh) 99.96%] was supplied by Merchem Ltd., Cochin, India. (b) Tetramethylthiuram disulfide (TMTD) Tetramethylthiuram disulfide (TMTD) is a secondary accelerator having the structure TMTD [Assay 97.6%, melting point C, loss on drying 0.25%, ash content 0.04%, oil content 1.13%] was supplied by Merchem Ltd., Cochin, India. (c ) N-cyclohexyl-2-benzothiazole sulphenamide (CBS) N-cyclohexyl-2-benzothiazole sulphenamide (CBS) is a fast accelerator having the structure CBS [melting point C, loss on drying 0.28%, ash content 0.09%, methanol insolubles 0.10%] was supplied by Merchem Ltd., Cochin, India Activators The activators used were zinc oxide and stearic acid supplied by Samira Chemicals, Coimbatore, India Plasticiser Dioctyl phthalate (DOP) was used as the plasticiser was supplied by Super Scientific Supplies, Coimbatore, India. 64

6 Fillers (a) Silica Silica used was ULTRASIL VN3 (containing 99 percent silicon dioxide (SiO 2 ) and a specific BET surface area of approximately 170 m 2 /g) manufactured by Evonik Degussa GmbH, Germany. (b) Carbon black Carbon black N550 FEF, manufactured by Philips Carbon Black Ltd., India having particle size nm, iodine number 43±5 mg/g and surface area m 2 /g was used. (c) Precipitated calcium carbonate Precipitated calcium carbonate of average particle size 0.7 micron was supplied by Nice Chemicals (P) Ltd., Cochin, India Other chemicals Coumarone-Indene resin (CI resin) with softening point of C was used as tackifier and was supplied by Ponmani and Co., Coimbatore, India. Diethylene glycol (DEG) with assay (GC) 99%, density (d 20 /4 ) and refractive index (at 20 C) was supplied by Nice Chemicals (P) Ltd., Cochin, India. 3.2 Preparation of NBR-nanofiller composites A two-step procedure was adopted to prepare NBR nanocomposites. In the first step, a masterbatch of NBR and nanofiller was prepared. In the second step, this masterbatch was added along with other compounding ingredients to prepare the NBR nanocomposites Preparation of NBR - nanofiller masterbatch The masterbatch of filler and NBR in the ratio 3 parts rubber to 1 part nanofiller by weight was made using Fissions Haake Rheocord 90. NBR was first masticated at 60 rpm till the torque stabilized. After the stabilization of torque, nanoclay was added and mixing was continued for 10 min. Masterbatches for nanoclay, nanocalcium carbonate and 65

7 carbon nanotubes were prepared separately. The masterbatch thus prepared was used in the second step to prepare NBR nanocomposites Preparation of NBR - nanofiller composites Neat NBR was first masticated with calculated quantities of NBR nanofiller masterbatch on a two roll mill of roll length 13 in. and roll diameter 6 in. The friction ratio was maintained at This was followed by addition of other compounding ingredients. The formulation for preparing NBR nanocomposites is given in Table 3.5. Table 3.5 Formulation for NBR nanocomposites Ingredient phr NBR (different ACN contents) 100 Sulphur 1.5 Zinc Oxide 5.0 Stearic Acid 1.0 Nanofiller (nanoclay, NCC or CNT) Dioctyl phthalate (DOP) varied varied MBTS 1.25 TMTD 0.25 The following designations were used to identify the various samples. NBR nanoclay composites : NBRNCLX NBR NCC composites : NBR NCCX NBR CNT composites : NBRCNTX where X is the amount of nanofiller. Thus NBRNCL5 indicates NBR nanoclay composite having a nanoclay content of 5 phr. For nanoclay and NCC, nanocomposites containing 0, 2, 5, 7.5 and 10 phr nanofiller were prepared. NBR CNT were prepared with 0, 0.5 and 2 phr CNT. 66

8 The rubber formulations were evaluated for cure characteristics on an oscillating disc rheometer (TechPro Rheotech ODR- ASTM D-2084). The NBR nanocomposites were compression moulded at 150 C and 200 MPa for the optimum cure time in a hydraulic press to make approximately 2 mm thick rubber sheets. 3.3 Characterization methods Cure characteristics The rubber formulations were evaluated for cure characteristics at 150 C on TechPro Rheotech oscillating disc rheometer (ODR) (ASTM D-2084). The time to attain 90% of the maximum rheometric torque was taken as the optimum cure time (t 90 ). Scorch time (t 2 ), minimum torque and maximum torque also were evaluated Wide angle X ray diffraction Wide Angle X-ray Diffraction (WXRD) was used to study the dispersion of nanoclay in the NBR matrix. X-Ray diffraction studies were performed at 3 /minute on Bruker D8 ADVANCE X-ray diffractometer with Cu X-ray beam of wavelength A. The diffraction patterns were recorded from 2θ = 3º to 13º. The interlayer distance of organoclay in the nanocomposite was determined from the position of diffraction peak in XRD diffractograms of using Bragg s law. nλ= 2d sinθ (3.1.) where n is an integer, λ is the wavelength, d is the d spacing and θ is the incident angle Transmission electron microscopy The morphology of the nanocomposites was examined by transmission electron microscopy (TEM) images taken with JEOL 2010 electron microscope with accelerator voltage of 200 kv. The nanocomposite samples for TEM analysis were prepared by ultra cryomicrotomy at -80 C using Leica Ultracut UCT. Freshly sharpened glass knives with cutting edge of 45 were used to get cryosections of 100 nm thickness. 67

9 3.3.4 Mechanical property measurements To evaluate the stress strain characteristics, ultimate strength, modulus and elongation at break dumbbell specimens were punched out from the2 mm thick moulded sheets and tested as per ASTM D412 method on a UTM at a crosshead speed 500 mm/min. Five specimens were tested in each case and the average values were reported. To measure the oil ageing properties, the dumbbell specimens were immersed in ASTM oil for 72 hours at room temperature and tested for mechanical properties. Three specimens were tested in each case and the average values were reported. To evaluate the heat ageing properties, the dumbbell specimens were subjected to heat ageing at 100 C for 48 hours and tested for mechanical properties. Three specimens were tested in each case and the average values were reported Dynamic mechanical analysis Dynamic mechanical analysis (DMA) was done using TA Instruments DMA Q800. Rectangular specimens having dimensions 35 mm x 12 mm x 2 mm were used. The storage modulus (E ), loss modulus (E ) and mechanical damping factor (tan δ) were evaluated by applying 0.01% strain on the sample. The dynamic analysis was carried out in dual cantilever mode with temperature scan from -70 C to +70 C using heating rate of 2 C/minute at frequency range 1 and 10 Hz Differential scanning calorimetry Differential scanning calorimetry was done on Mettler Toledo DSC 822e in the temperature range -100 C to 300 C at a heating rate of 10 C/minute Thermogravimetric analysis The thermal stability of the samples from 35 to 500 C was investigated by thermogravimetric analysis (TGA) using NETZSCH STA 409 CD TGA-DTA simultaneous analyzer at a heating rate of 10 C/minute in nitrogen atmosphere. 68

10 3.3.8 Gas permeation rate The gas permeation rate through the nanocomposites were tested using Lyssy L manometric gas permeability tester with oxygen gas at 10 ml/hour and 23 C Solvent sorption experiments Transport properties were studied using rectangular samples of size 20 mm x 20 mm x 2 mm that were cut from the NBR nanoclay composites. The edges of the samples were slightly curved to obtain uniform absorption. The thickness and initial weight of samples were measured. The samples were completely immersed in toluene in glass diffusion bottles kept at uniform temperature. The samples were removed from the solvent at specific time intervals, excess solvent at the surface removed using filter paper and weighed. The samples were returned to the solvent in the diffusion bottle immediately. The process was continued until equilibrium swelling is reached. At time t of immersion, the mole percent uptake Q t for solvent was determined using the formula Q t ( M M ) t 0 MW = x100 (3.2) M 0 where M t is the mass of sample after time t of immersion, M o the initial mass of the sample and M W is the molecular weight of the solvent. The sorption isotherms were plotted with the mole percentage uptake of solvents for the nanocomposites versus square root of time. The diffusion and permeability coefficients were then calculated. The experiments were conducted at 30, 50 and 70 C. The values reported here is the average of three experiments. 69